1. Field of the Invention
The present invention relates to a manufacturing method of manufacturing methods of superconducting material and product and superconducting material.
2. Description of the Prior Art
In manufacturing superconducting material or product, there have been generally employed methods to be specifically described next.
In a first manufacturing process P1, a fine powderly primary material m1, as a raw material of superconducting material, is primarily milled and mixed at a dry type milling mixer at step S1. Next, at step S2, the milled primary material m1 obtained from the step S1 is heat-processed. Then, at step S3, the heat-processed material from the step S2 undergoes a secondary milling/mixing process to become a secondary material m2.
In a second process P2 for obtaining a superconducting material M1, after the above process P1, the secondary material m2 is molded at step S4 and then baked at step S5.
In a third process P3 for obtaining a superconducting wire product M2, the secondary material m2 from the process P1 is filled into a pipe at step S6. Then, this pipe undergoes a wire drawing process at step S7, and the secondary material m2 in the wire-drawn pipe is sintered at step S8.
In a fourth process P4 for obtaining a powderly target material M3 for forming a superconducting thin film, the secondary material m2 from the process P1 is molded at step S4 and then baked at step S5.
According to the prior art, in order to obtain a superconducting product or a superconducting wire product, a dry type milling/mixer such as shown in FIG. 12. This milling/mixer includes a casing 35 which is maintained still or rotated at a slow speed in operation and milling elements 36 disposed inside the casing 35 and rotated at a slow speed about an axis P. In operation, the primary material m1 is milled between the bottom surface of the casing 35 and the milling elements 36, and at the same time, with the rotation of the milling elements 36, the material m1 is stirred and mixed, whereby the primary milling/mixing process S1 and the secondary milling/mixing process S3 are effected.
Further, the heat-processing step S2 and the secondary milling/mixing step S3 are repeated no less than 3 to 4 times, thereby causing a preliminary solid phase reaction and eliminating gaseous matters and inpurities at the heat-processing steps S2 and effecting milling and particle-size-averaging operations at the secondary milling/mixing step S3.
With the above-described conventional milling/mixer; however, the milling of the primary material m1 is effected only by pressing the same against the bottom surface of the casing 35 by means of the milling elements 36, whereby the particle size distribution efficiency is extremely low. With such low efficiency, the heat-processing step S2 and the primary and secondary milling/mixing steps S1 and S3 need to be repeated for three to four times, and even after the repetition of these steps, a superconducting material or product obtained from this processed secondary material achieves only low performance. In short, the above conventional milling/mixer has suffered from high running costs and time-consuming and troblesome operations. Moreover, with the secondary milling/mixing step S3 using the conventional device, there occurs a great amount of irregularity in the particle size. Accordingly, if the secondary material m2 with such particle size irregularity is filled in the pipe at step S6, there tends to occur a great number of voids in the material filled in the pipe, which results in disadvantageous unevenness in the concentration of the material m2 in the wire drawing operation subsequently effected at step S7. Needless to say, such uneven material concentration easily leads to deterioration in the electric current density when the material is sintered at step S8.
On the other hand, for manufacturing a target material for forming a superconducting thin film, the prior art has used a dry type milling/mixer such as shown in FIG. 13. This milling/mixer is essentially a ball mill having a drum type casing 38 to be slowly rotated about a horizontal axis and a plurality of balls 37 freely movably held in the casing 38. In operation, with a rotation of the casing 38, the primary material m1 is stirred and milled between the balls 37 each other or between the balls 37 and the casing 38, thereby effecting the primary milling/mixing step S1 and the secondary milling/mixing step S3.
However, the primary and second milling/mixing steps S1 and S3 using the above-described ball mill are very inefficient and therefore very time-consuming. Moreover, because of the inefficient and insufficient mixing effect, the obtained target material often fails to satisfy the requirement of extremely even particle size distribution and concentration for forming a high-quality superconducting film.
The first object of the present invention is to provide an improved manufacturing method of a secondary material for a high-quality superconducting product or wire product having a sufficiently high electric current density or for a target material for forming a high-quality superconducting film.
Again, according to the prior art, the fine powderly secondary material m2 obtained from the secondary milling/mixing steps S3 was not coated. However, such un-coated secondary material m2, if stored for a long period, often shows a quality deterioration due to oxygen or moisture existing in the ambient air.
With view to this problem, the second object of the present invention is to provide an improved fine powderly secondary material m2 of a superconducting material which may effectively resist such quality deterioration due the oxygen or moisture in the ambience through an extended storage period.
Further, in the prior art of obtaining a superconducting mold product, the secondary material m2 after the secondary milling/mixing steps S3 is mixed with such a binder as PVA and then this mixture is baked at step S5. However, since a sintering process takes place after molding with the binder the secondary material m2 which has been only baked, the sintering process often accompanies significant thermal contraction or distortion, which makes it difficult to control the shape or size of the superconducting product with high precision. Consequently, if the superconducting product is to acquire a complicated shape which requires such high manufacturing precision, the prior art has been unable to produce such products on a mass-production scale.
Thus, the third object of the present invention is to provide a manufacturing method which makes it possible to easily produce a superconducting product even if the product is to acquire a complicated shape.
In the prior art of obtaining a superconducting wire product, in the sintering process of step S8, the pipe is made from Ag in order to avoid any undesired reactions between the secondary material m2 and the pipe. Also, if the material m2 contains Y, O.sub.2 is fed into the pipe over a long period so that the fed O.sub.2 diffuse inside the pipe to effectively maintain the rhombic system of the material components. Naturally; however, Ag pipe is very costly and moreover, the pipe of such good conductor as Ag prohibits its use with an alternating current system. Moreover, the feeding of the O.sub.2 into the pipe of small diameter is extremely difficult.
In view of the above state of the art, the fourth object of the present invention is provide a manufacturing method of superconducting wire product, which method permits formation of pipe with inexpensive and non-conductive material and which eliminates the necessity of feeding of O into the pipe.